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Mechanism of Permanganate-Promoted Dihydroxylation of Complex Diketopiperazines: Critical Roles of Counter-cation and Ion-Pairing.
Haines, Brandon E; Nelson, Brandon M; Grandner, Jessica M; Kim, Justin; Houk, K N; Movassaghi, Mohammad; Musaev, Djamaladdin G.
Afiliación
  • Haines BE; Cherry L. Emerson Center for Scientific Computation and Department of Chemistry , Emory University , Atlanta , Georgia 30322 , United States.
  • Nelson BM; Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
  • Grandner JM; Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095-1569 , United States.
  • Kim J; Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
  • Houk KN; Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095-1569 , United States.
  • Movassaghi M; Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
  • Musaev DG; Cherry L. Emerson Center for Scientific Computation and Department of Chemistry , Emory University , Atlanta , Georgia 30322 , United States.
J Am Chem Soc ; 140(41): 13375-13386, 2018 10 17.
Article en En | MEDLINE | ID: mdl-30295476
The mechanism of permanganate-mediated dual C-H oxidation of complex diketopiperazines has been examined with density functional theory computations. The products of these oxidations are enabling intermediates in the synthesis of structurally diverse ETP natural products. We evaluated, for the first time, the impact of ion-pairing and aggregation states of the permanganate ion and counter-cations, such as bis(pyridine)-silver(I) (Ag+) and tetra- n-butylammonium (TBA+), on the C-H oxidation mechanism. The C-H abstraction occurs through an open shell singlet species, as noted previously, followed by O-rebound and a competing OH-rebound pathway. The second C-H oxidation proceeds with a second equivalent of oxidant with lower free energy barriers than the first C-H oxidation due to directing effects and the generation of a more reactive oxidant species after the first C-H oxidation. The success and efficiency of the second C-H oxidation are found to be critically dependent on the presence of an ion-paired oxidant. We used the developed mechanistic knowledge to rationalize an experimentally observed oxidation pattern for C3-indole-substituted diketopiperazine (+)-5 under optimal oxidation conditions: namely, the formation of diol (-)-6 as a single diastereomer and lack of the ketone products. We proposed two factors that may impede the ketone formation: (i) the conformational flexibility of the diketopiperazine ring, and (ii) hindrance of this site, making it less accessible to the ion-paired oxidant species.
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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Óxidos / Oxidantes / Compuestos de Manganeso / Dicetopiperazinas Tipo de estudio: Prognostic_studies Idioma: En Revista: J Am Chem Soc Año: 2018 Tipo del documento: Article País de afiliación: Estados Unidos Pais de publicación: Estados Unidos
Texto completo
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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Óxidos / Oxidantes / Compuestos de Manganeso / Dicetopiperazinas Tipo de estudio: Prognostic_studies Idioma: En Revista: J Am Chem Soc Año: 2018 Tipo del documento: Article País de afiliación: Estados Unidos Pais de publicación: Estados Unidos